A gas separation method employing a membrane has a higher energy efficiency than other gas separation methods. Further, such a gas separation method has a simple apparatus structure. For these reasons, such a gas separation method is now applied in the separation of various gases.
The most typical aspect of the gas separation membrane forms a thin film of a gas separating resin on a surface of a porous support member. This aspect is effective as a large gas permeation amount can be achieved while providing a certain level of strength to the gas separation membrane.
Recently, among gas separation membranes, it has been tried to employ a gas separation membrane which utilizes the difference between the permeability of oxygen and nitrogen in an internal combustion engine system (e.g., see Patent Document 1). This utilization method is effective in cleaning the exhaust gases in the internal combustion engine system, and in improving fuel consumption. Further, according to this utilization method, it is thought that recent environmental problems caused by exhaust gases and carbon dioxide gas can be comparatively easily resolved. For these reasons, this utilization method is attracting attention.
Patent Document 2 describes a gas permeation membrane which includes a porous support member having an ultrafiltration membrane structure.
Further, Patent Document 3 describes a gas separation membrane coated with an amorphous fluorocarbon polymer on one side of a porous support membrane composed of a polytetrafluoroethylene resin or a polyolefin resin.
In addition, Patent Document 4 describes a monolayer gas separation membrane, which has an oxygen/nitrogen separation coefficient of 1.4 or more, obtained by forming a film of a perfluorodioxole binary copolymer and then subjecting the produced film to melt-compression molding.
Patent Document 1: Japanese Patent Laid-Open No. 2002-122049
Patent Document 2: Japanese Patent Examined Publication No. 6-96107
Patent Document 3: WO90/15662 Pamphlet
Patent Document 4: Japanese Patent Laid-Open No. 10-99665